1. Field of the Invention
The present invention is directed to data networking, and, more particularly, to secure, portable, and wireless data networking.
2. Description of the Related Art
In the current Wireless Local Area Network (WLAN) architecture, mobile clients connect wirelessly to Access Points (APs) to acquire connectivity to a backbone network to which the APs are attached. The backbone network is typically wired and is then connected to the rest of the organizational network. Among different WLAN communication standards, IEEE 802.11 (“Part 11: Wireless LAN Medium Access Control (MAC) and physical layer specifications”, IEEE, 1999, and including all variations) is currently the most popular.
The WLAN architecture is ideal for network administrators who wish to wirelessly extend the boundary of their existing wired campus or corporate networks and to provide campus-wide mobility support. Under this architecture, mobile clients are no longer constrained by network cables and wall jacks as long as they maintain direct wireless contacts with some AP. Thanks to a number of dynamic configuration protocols such as the Dynamic Host Configuration Protocol (DHCP) (R. Droms, “Dynamic Host Configuration Protocol,” RFC 2131, March 1997), mobile clients can easily join the WLAN with little or no user configuration effort. A user can move freely within the coverage area of the APs. When the user moves across the boundaries of the service areas of APs, WLAN and bridge protocols can update the link layer connectivity for the user so that on going communication sessions are not interrupted by the handoff and actual communication carrier (radio frequency) switch.
While mobile clients can enjoy the convenience of wireless network connectivity, on the other hand, it is not a trivial task to deploy a WLAN. APs need to be interconnected via a backbone network, typically a wired LAN. Therefore network cables must be installed to connect the APs to the existing network infrastructure. Electrical wires must also be in place to supply operating power to the APs. In addition, in order to determine the locations for the APs, WLAN planners need to predict wireless usage and conduct site surveys to determine the radio propagation characteristics. Operating channels also need to be allocated to each AP to keep the interference between neighboring communication cells to a minimum. After the deployment, it becomes another costly task to change the placement of the APs since the cables and wires need to be changed as well. If the usage pattern changes, oftentimes the WLAN is not able to be dynamically reconfigured to adapt to the changes.
Another problem with the existing IEEE 802.11 WLAN lies in its current security mechanism. In a WLAN, all transmitted bits are delivered over the air, which is an open communication medium to which anyone has access if he/she is within the radio signal range and has a radio device capable of receiving WLAN radio signals. Thus, encryption must be applied to sensitive data so that only the intended recipients can reconstruct and comprehend the data.
The IEEE 802.11 standard relies on the Wired Equivalency Privacy (WEP) protocol for its data protection. WEP uses a shared secret key of 40 bits (or 104 bits in a later version). A 24 bit Initial Vector (IV) is concatenated with the shared key to create a 64 bit (or 128 bit in the later standard) seed. The seed is then fed to a RC4 Pseudo Random Number Generator (PRNG) to generate a random bit sequence, which is used as the frame encryption key stream. The IV may be changed for every data frame encrypted so that the seed for the RC4 PRNG is different for every data frame. Thus, a different key stream is generated for encrypting each data frame. The IV is enclosed as clear text in each data frame so that the receiver may concatenate the received IV with the shared secret key to produce the RC4 PRNG seed and compute the decryption key stream. However, due to the limited IV size, there are only 2^24, about 16 million, distinct key streams. Given the size of an average data frame and the transmission rate supported by IEEE 802.11, a busy AP may exhaust the distinct key stream space very quickly and be forced to reuse the encryption key stream. Since the IVs are enclosed as clear text in each data frame, it is relatively easy for an attacker to recognize a reused key stream. The attacker may collect pieces of cipher text that are encrypted with the same key stream and perform statistical analysis to attack and recover the plaintext. An attacker may also build up a dictionary of all possible key streams. In addition to vulnerabilities to these types of attacks, the security research community has also identified other weaknesses of the WEP protocol (N. Borisov, I. Goldberg, and D. Wagner, “Intercepting Mobile Communications: The Insecurity of 802.11”, MOBICOM 2001, 2001).
The authentication scheme of IEEE 802.11 also has known problems that are related to the weaknesses in its encryption scheme. IEEE 802.11 APs provide two methods to protect against unauthorized accesses: Medium Access Control (MAC) address filtering and WEP-based shared-key authentication. A MAC address filter simply drops all data frames whose destination or source addresses are not listed in a pre-defined “allowed list”. However, because MAC addresses can easily be sniffed and forged by any attacker, the MAC address filter offers little protection against unauthorized network accesses. The shared-key authentication process involves both parties (named initiator and responder) encrypting the same challenge using WEP with the same shared-key but different IVs. Since the shared-key authentication algorithm authorizes network access to those who have the shared-key, it would be effective only if unauthorized parties cannot recover the shared-key. However, with WEP being breakable, the shared-key authentication becomes only an illusion.
The IEEE's 802.1x (Port Based Network Access Control) standard (“Port-Based Network Access Control”, IEEE, 2001) specifies an architectural framework that is designed to provide user authentication, network access control, and dynamic key management. Within the IEEE 802.1x framework, a system can use various specific authentication schemes and algorithms. The actual algorithm that is used to determine whether a user is authentic is left open and multiple algorithms are possible. After the exposure of the weaknesses in the IEEE 802.11 security mechanism, organizations have moved rapidly to adopt IEEE 802.1x as a solution for fixing the security problems in wireless LANs. The IEEE Robust Security Network (RSN) has also included the IEEE 802.1x standard as an important component (802.11i, IEEE 802.11 Task Group I, work in progress).
IEEE 802.1x is based on the PPP Extensible Authentication Protocol (EAP, L. Blunk and J. Vollbrecht, “PPP Extensible Authentication Protocol (EAP)”, RFC 2284, March, 1998) for message exchange during the authentication process. EAP is built around the challenge-response communication paradigm that is common in network security solutions. Although originally designed as an authentication method for PPP connection, it can also be used for a wide range of LAN types such as Ethernet, token ring, or WLANs.
The following is a description of 802.1x-based authentication and dynamic encryption. FIG. 1 shows the components involved in IEEE 802.1x authentication operations. In a WLAN 100 with IEEE 802.1x, a client (also known as a supplicant) 102 requests access service to an AP (or an authenticator) 104. The AP 104 opens an unauthorized port for the client 102, which only accepts EAP messages from the supplicant (client) 102. Through this unauthorized port, the supplicant 102 exchanges EAP messages with the authenticator 104 and the authentication server 106, which is a backend server executing the authentication algorithms. At the end of the authentication algorithm, the authentication server 106 returns an “accept” or “reject” instruction back to the authenticator 104. Upon receiving an “accept” message, the AP 104 opens the regular network access port for the client 102 to allow normal traffic for this client 102 to go through.
IEEE 802.1d MAC Bridge protocol (“Part 3: Media Access Control (MAC) Bridges”, IEEE, 1998 (IEEE 802.1d); “Part 3: Media Access Control (MAC) Bridges—Amendment 2: Rapid Reconfiguration”, IEEE, 2001 (IEEE 802.1w)) is known in the art.
IEEE 802.1d employs a spanning tree protocol, which is its method of forming a packet forwarding topology while preventing forwarding loops within a network of bridging devices. In an arbitrarily connected network, each bridge includes multiple ports. These ports are attached to a number of LAN segments. Among all bridges in a network, one bridge acts as the “root” of the spanning tree. It is the bridge with the highest priority bridge identifier (the priority identifier of a bridge is either derived from the unique ID of the bridge, which is typically the lowest MAC address among those of the bridge's ports, or configured by the network administrator).
In this protocol, each bridge uses each of its ports to report the following to its neighboring bridges: its own identity, the identity of the transmitting port, the identity of the bridge that the transmitting bridge believes to be the root, and the cost of the path from the transmitting port to the root bridge. Each bridge starts by assuming itself to be the root. If a bridge receives information that is “better” than what it currently has, it will re-compute its information based on the newly received information and then send out updated control messages to its neighboring bridges. What is considered “better information” includes information such as a bridge being a better root (with higher priority bridge identifier), a shorter path towards the root, lower cost routes, etc. Eventually through information propagation, all bridges learn the active spanning tree topology and configure their ports to forward data frames accordingly. On each bridge, the port that is the closest to the root is known as the “root port”. On each LAN segment, the bridge that can provide the shortest path towards the root is known as the “designated bridge” for the LAN segment.
The IEEE 802.11 standard is known in the art.